The present invention relates to a novel evaluation method of the golf club different from a conventional method, and a golf club evaluated by the evaluation method. More particularly, the present invention relates to a evaluation method of the golf club capable of showing flexibility felt by a golfer more accurately than in the conventional case, and a golf club evaluated by this evaluation method. Alternatively, the present invention relates to an evaluation method of the golf club capable of showing a hit ball height presented by a golf club more accurately, and a golf club evaluated by the evaluation method.
The golfer tries to improve his/her skills for better golf playing. However, on the other hand, much depends on golf clubs to be used. Thus, better performance is always required of the golf clubs. To provide better performance golf clubs, especially since bending occurs in a club shaft constituting a golf club during swinging, physical performance such as flexibility felt by the golfer is greatly influenced by the bending.
Therefore, in order to provide a golf club having optimal flexibility to the golfer, the degree of flexibility has been expressed quantitatively, i.e., in numerical values. Various studies have been made, particularly on the frequency of the club shaft from early times.
For example, Japanese patent application Kokai publication No. 52-126321 discloses a technology for establishing harmony in frequency among the shafts of golf clubs in a set. In this case, in the set including a plurality of golf clubs, the harmony is obtained by selecting a proper club shaft in such a way as to set a plot between a shaft frequency and a shaft length at a specified gradient, and combining this club shaft with a specified club head.
Japanese patent application Kokai publication No. 1-285276 discloses a technology for increasing a carry and reducing mistaken shots. These objects are achieved specifically by deciding an optimal frequency intrinsic to a golfer from his/her swinging characteristic, and selecting a golf club having an optimal frequency based on this optimal intrinsic frequency.
In addition to the above technologies in the conventional art, generally, the numerical values of frequencies regarding the club shafts or golf clubs have widely been used. The method of measurement for frequencies was carried out as follows. That is, in the case of the club shaft, a frequency was measured by attaching a weight to the tip portion of the club shaft, i.e., a head portion with a rear end fastened, in other words, a grip portion. On the other hand, a frequency was measured by fastening the rear end portion of the grip.
The frequency measurement of the club shaft has basically been performed mainly by a golf club manufacturer, or a club shaft manufacturer. Performance evaluation was made for a single club shaft, and the result thereof was reflected on a golf club. The frequency measurement of the golf club has been very general, and carried out even at a golf shop or the like. The result thereof has been considered as one of the performance evaluations of the golf clubs.
The performance evaluation of the club shaft or golf club mainly means evaluation on club shaft flexibility. In the case of club shafts, if the lengths are equal, as a numerical value of a frequency is larger, the shaft is evaluated to be stiffer. The golf club manufacturer or the like has referred to the numerical value of a club shaft frequency, and thereby decided to reduce the frequency of the golf club by attaching a heavy club head to the club shaft, or conversely to increase the frequency of the golf club by attaching a light club head to the club shaft. In other words, the frequency of the club shaft has been used for a part of a development process designed to predict golf club characteristics based on evaluation for each component of the golf club.
If the lengths of the golf clubs are equal, a club having a larger numerical value of frequency is generally suited for a fast head speed golfer, since a stiffer feeling is provided as the numerical value of a frequency is larger. A club having a lower numerical value of frequency is generally suited for a slow head speed golfer, since a more flexible feeling is provided as the numerical value of frequency is smaller. The golf club manufacturer, the golf shop or the like has indicated the frequency numerical value of each golf club as the index of the feeling of flexibility, and the user has purchased a golf club by using such an index as a yardstick.
However, noncoincidence often occurred between the numerical value of a frequency and flexibility actually felt by the golfer. For example, when the golfer who used the golf club having a metallic golf shaft attached thereto changed it to the golf club having a fiber reinforced resin club shaft attached thereto, a change often occurred also in the feeling of flexibility.
Such a phenomenon was not due to a mere difference between the metallic club shaft and the fiber reinforced club shaft, because the phenomenon was observed between the metallic club shafts or between the fiber reinforced club shafts. In addition, even between similar club heads, equal club shaft masses, equal golf club masses and equal golf club lengths, the phenomenon was observed because of a difference between the club shafts.
With regard to noncoincidence between the numerical value of a frequency measured in the conventional art and the flexibility actually felt by the golfer, the inventors paid attention to a longitudinal stiffness distribution among club shafts. More specifically, in the conventional method of measurement, in the case of golf clubs having equal lengths, there is a tendency that the numerical value of a frequency is smaller as the stiffness of a rear end portion is lower, and the numerical value of a frequency is larger as the stiffness of a tip portion is lower.
As described above, in the conventional evaluation method for measuring a frequency by fastening the rear end portion of the club shaft and then evaluating the flexibility of the golf club based on the numerical value of the frequency, depending on a difference in a stiffness distribution among the golf clubs, there has been cases where the frequency was small even in the golf club actually felt stiff by the golfer, and the frequency was large even in the golf club actually felt flexible by the golfer. Thus, the expression of the flexibility actually felt by the golfer based on the numerical value of a frequency used in the conventional evaluation method was not sufficient.
The above tendency has been particularly conspicuous in the fiber reinforced rein club shaft that has been popular in recent years. As a result, an opinion has recently taken precedence that the numerical values of frequencies should be used only for reference without any excessive dependence thereon.
The object of the present invention is to provide an evaluation method of a golf club, capable of more accurately showing the characteristic of a club shaft. More particularly, the object of the present invention is to provide an evaluation method of a golf club, capable of showing flexibility felt by a golfer more accurately than in the conventional case, and a golf club evaluated by the evaluation method. Alternatively, the present invention provides an evaluation method of a golf club, capable of more accurately showing the height of a hit ball presented by a golfer, and a golf club evaluated by the evaluation method.
In order to achieve the foregoing object, in accordance with a first aspect of the present invention, the evaluation method of a golf club comprises the steps of: measuring a frequency per unit time by vibrating a rear end portion while keeping a tip portion of a club shaft in a fastened state; and evaluating a golf club using the club shaft based on the frequency.
As a result of zealous studies, the inventors discovered that the frequency measured by vibrating the rear end portion while keeping the tip portion of the club shaft in a fastened state is useful for accurately understanding the characteristic of the club shaft, and came up with the present invention.
The frequency measured by vibrating the rear end portion while keeping the tip portion of the club shaft in a fastened state can be singly used for evaluation of the golf club, or can be used for the same purpose in combination with a frequency per unit time measured by vibrating the tip portion while keeping the rear end portion of the club shaft in a fastened state. In other words, while the frequency per unit time is measured by vibrating the tip portion with the rear end portion of the club shaft kept in a fastened state, the frequency per unit time is measured by vibrating the rear end portion with the tip portion of the club shaft kept in a fastened state and, based on the calculated values of these frequencies, the golf club using the club shaft can be evaluated.
In order to achieve the foregoing object, in accordance with a second aspect of the present invention, the evaluation method of a golf club comprises the steps of: measuring a frequency per unit time by vibrating a tip portion while keeping a rear end portion of a club shaft in a fastened state; measuring a frequency per unit time by vibrating the rear end portion while keeping the tip portion of the club shaft in a fastened state; and evaluating a golf club using the club shaft based on the sum of these frequencies.
As a result of zealous studies, the inventors discovered that there is a correlation between the sum of the frequency measured by vibrating the tip portion while keeping the rear end portion of the club shaft in a fastened state and the frequency measured by vibrating the rear end portion while keeping the tip portion of the club shaft in a fastened state and flexibility actually felt by a golfer, and came up with the present invention.
By evaluating the golf club based on the sum of such frequencies, flexibility felt by the golfer can be shown more accurately than in the conventional case.
In order to achieve the foregoing object, in accordance with a third aspect of the present invention, the evaluation method of a golf club comprises the steps of: measuring a frequency of per unit time by vibrating a tip portion while keeping the rear end portion of a club shaft in a fastened state; measuring a frequency per unit time by vibrating the rear end portion while keeping the tip portion of the club shaft in a fastened state; and evaluating a golf club using the club shaft based on the ratio of these frequencies.
As a result of zealous studies, the inventors discovered that there is a correlation between the ratio of the frequencies measured by vibrating the tip portion while keeping the rear end portion of the club shaft in a fastened state and the frequency measured by vibrating the rear end portion while keeping the tip portion of the club shaft in a fastened state and a height of a hit ball actually presented by the golf club, and came up with the present invention.
By evaluating the golf club based on the ratio of such frequencies, the height of the hit ball presented by the golf club can be shown more accurately.
In the above measurement of frequencies, a weight may be attached to the end portion of the club shaft to be vibrated. In other words, a frequency per unit time can be measured by vibrating the tip portion while keeping the rear end portion of the club shaft in a fastened state and the weight attached to the tip portion. In addition, a frequency per unit time can be measured by vibrating the rear end portion while keeping the tip portion of the club shaft in a fastened state and the weight attached to the rear end portion.
On the other hand, the golf club of the present invention includes a club head attached to the tip portion of the club shaft, and a grip or a grip portion provided in the rear end portion. In this case, the golf club is evaluated based on the sum of the frequency per unit time measured by vibrating the tip portion while keeping the rear end portion of the club shaft in a fastened state and the frequency per unit time measured by vibrating the rear end portion while keeping the tip portion of the club shaft in a fastened state.
According to the golf club evaluated based on the sum of such frequencies, flexibility felt by the golfer can be recognized more accurately than in the conventional case.
The golf club of the present invention includes a club head attached to the tip portion of the club shaft, and a grip or a grip portion provided in the rear portion. In this case, the golf club is evaluated based on the ratio of the frequency per unit time measured by vibrating the tip portion while keeping the rear end portion of the club shaft in a fastened state and the frequency per unit time measured by vibrating the rear end portion while keeping the tip portion of the club shaft in a fastened state.
According to the golf club evaluated based on the ratio of such frequencies, the height of a hit ball presented by the golf club can be recognized accurately.
Means for providing evaluation based on the sum or the ratio of the frequencies like that described above for the golf club can be optionally selected. According to first means, a value showing the sum or ratio of the frequencies can be indicated in a part of the golf club. According to second means, reference information for recognizing the value of the sum or ratio of the frequencies can be used. According to third means, the value showing the sum or ratio of the frequencies can be set corresponding to the model of the golf club. In any means, the evaluation of the golf club can be easily understood based on the sum or ratio of the frequencies.
In the present invention, there should be no particular limitation placed on the unit time of a frequency. For example, a frequency (cpm) per minute or a frequency (Hz) per second, can be measured. Generally, since a frequency (cpm) per minute is used in the golf industry, the present invention will be described by using a frequency (cpm) per minute, for facilitating understanding.